The present invention generally relates to a storage apparatus for storing database and a computer system for managing the storage apparatus, and particularly to a recovery method for the operation of recovering the tables used in the database.
A large-scale information processing system employs database in order to effectively manage the data used in the information processing system. In general, the database has a plurality of tables, and the information processing system converts these tables into tables with aimed data (this process is hereinafter called “table conversion”) by executing a program (hereinafter, referred to as “data conversion batches” or “data conversion jobs”), and uses the tables obtained after the conversion.
At this time, a computer for executing the data conversion batches in the information processing system acquires data that constitutes a table from a storage apparatus in which the data is stored. Then, the computer makes the table conversion and writes the converted table into the storage apparatus. In this case, the converted table is stored in a particular storage region (hereinafter, referred to as “volume”) of the storage apparatus for each application of that table.
If the computer, which is executing the data conversion batches for the data conversion, abnormally ends, stops or intermits this process, the data of the table on which the computer is making the conversion process causes a mismatch or inconsistency, which leads to the inconsistency of data of the whole information processing system. In this case, the information processing system is required to restore the data of this inconsistent table to its original data, or the state in which the table is not converted yet, and again to execute the table conversion.
In order to make the above data-restoring process, the system administrator has so far ordered the computer, for managing tables, to execute a program (hereinafter, also called “database management system (DBMS)” to produce converted tables, at which time the execution history (hereinafter, referred as “log”) can also be acquired in advance. In the event that a trouble occurred, the computer utilized this log to restore the table (for example, see “Database Processing”, written by D. M. Kroenke, 1996, p. 524).
In another method, the system administrator previously produces in the storage apparatus the copy (hereinafter, called “backup”) of the volume in which the table not converted yet is stored, and uses the backup of the volume, when a trouble occurs, to restore the original table, so that the failed or inconsistent table can be swiftly restored to the initial state.
The conventional methods have the following drawbacks.
The recovery method using only the log, because it causes the computer to produce the log while making the table conversion, is obliged to apply the additional load for taking the log on the computer, with the result that the table conversion process couldn't be speeded up. In addition, when the failed table is restored to the original state, the computer processes the data of the table one after another on the basis of the log data from the start to recover, and thus it takes a long time to restore so that it is difficult to recover fast.
In the recovery method using the backup, because it acquires the backup before the table conversion is performed, it is difficult for the system administrator to restore the data of the failed table to the most recent state, or the state in which the recovered data can reflect the process executed just before the abnormal stop due to a failure in the computer.